Accelerometers have come to be used not only as a means for detecting changes of velocity of a device to which they are attached but as a means for detecting the position or attitude of a device to which they are attached (the host device). In the prior art accelerometers, a large coil for torque, or motor effect, has been employed. On one side of the frame holding said large coil there has been mounted a mass member. The mass member and the large coil have been designed to have a rotational movement into a magnetic flux field. The mass member responds to forces exerted on the host device (such as a change of inertia), or to a position or change of position of the host device (in response to gravity force). Such an accelerometer has a means to detect a change of position of the mass member and generate an "error" indicating such a change. The "error" signal so generated is transmitted to the large coil and a motor effect, or torque, is generated whereby the coil, and thus the mass, is moved to a point where torque matches the force applied. The accelerometer circuitry measures the error signal as an indication of the force on, or of a position of, the host device.
In the prior art accelerometer the mass has been attached to a frame which held the large coil. The frame has had two pivots mounted thereon and the pivots have been mounted onto two jewels. The jewel mounting means has a cup configuration. One of the major problems with the foregoing prior art design is that the mass hanging from the coil frame tends to distort the frame because of the lever effect of the weight (force) and the arm between the mass and the frame. With or without the distortion the weight, or mass, applies a force to the pivots which tends to move them to one side of the cupped jewel housing. This unbalance causes the pivots to wear per se and wear the jewel mounting as well. Accordingly the mountings holding the coil develop a loose fit, or "slop," and the frame starts to spuriously move laterally, without forces being applied, or in combination with forces being applied. The spurious lateral movement enables the mass member to move into incorrect and inconsistent positions relative to the electrical detection and spurious "error" signals are very often generated.
To overcome the foregoing problem the jewel mountings have been spring loaded to force the jewel mountings against the pivots. This solution of course added to the friction force between the jewel and the pivot and eventually caused more wear. The lifetime (before repair) of such prior art devices has been in terms of hours.
In addition, in the prior art, the circuitry employed a high frequency oscillator and an AM detector along with some elaborate interconnecting circuits. This prior art circuitry generated a substantial amount of RF noise. Accordingly, if such an accelerometer were used in aircraft or on shipboard or the like, the RF noise has been found to be undesirable.
The present device eliminates the problem of excessive wear at the pivot points and hence, eliminates the resulting spurious signals described above. In addition the present invention reduces the distortion of the coil frame and virtually eliminates the RF noise problems. Further in addition, the present invention improves the sensitivity and reduces the required hardware.